Characterization of local lymphoid cell responsiveness has been achieved and proposed work includes separation of lymphoid cells, from different lymphoid centers, into the various immunoglobulin class according to their surface receptors and the transfer of these to syngeneic recipients to determine the protective capacity of each lymphoid cell population. Parallel work in mice will assess the role of "T" cells using specific anti-theta serum. An immunogen obtained during the culture of third stage larvae to the fourth stage has been identified as a "protective" antigen. This immunogen will be separated by chromatography and immunoabsorption techniques, assessed for its immunizing capacity and characterized by physical and immunochemical methods. Using complement deficient guinea pigs (C1/4 deficient), immune mediated lesions and damage to the parasite will be studied. Particular attention will be paid to the acute inflammatory response on initial invasion.